Kevin Korth <kkorth at cyberhighway.net> wrote:
> This is, once again, proof that it's easier to print than to
> retract...feathers in the wind, so to speak.
>> I'm working entirely off memory, so hopefully some other posters will
> provide the appropriate references (or call Barbara Hemmingsen at San Diego
> State University, she know's this by heart). Several years ago a group of
> microbiologists working on hydrothermal vents at extreme depths published a
> paper claiming that they'd discovered this "hyperthermophile" that could
> live temps over 200*C. Naturally the press went wild with this story and it
> made it "scientific fact." What is usually not told is that shortly
> thereafter a group of microbiologists reviewing the study and attempting to
> replicate it discovered that the experimental design was riddled with errors
> and that they had not done the proper controls. They had, in fact,
> discovered nothing. What they were seeing was an artifact of a poorly
> designed experiment. Unfortunately, the press didn't jump on the bandwagon
> of the new findings and even today textbooks reference this imaginary
> hyperthermophile as fact.
>> I always get a chuckle when I see references to this imaginary organism...a
> lesson in science and the press.
>Kevin Korth is perfectly right. To my knowledge, some hyperthermophiles
are known that can stand 110°C or slightly above. This is the
temperature range of their survival. They can divide and propagate at
105°-1O8°C or so, if I remember well. Only some bacterial endospores can
resist for a while to 125-130°C. They are specialized cells with thicker
wall, lower water content and a certain number of biochemical properties
allowing some enhancement of the stability of DNA and proteins. Spores
do not divide, they just wait for milder conditions allowing them to
germinate and produce vegetative cells again.
Indeed the occurence of living cells at 200-300°C was shown to be a
tale. At such high temperatures, neither proteins or other cell
components can be preserved since many bonds would be broken.
Fragmentation and isomerizations of biological macromolecules can only
lead to a real mess within living matter. Any laboratory worker knows
that some sugars such as glucose may react very rapidly with proteins
giving brown degradation products (Maillard reaction). One of the main
difficulties living organisms have to cope with at elevated temperatures
is the stability of DNA. The double helix of DNA gets denatured, with
separation of the two strands. This occurs between 70 and 110°C
according to the base composition. Hyperthermophiles seem to have
molecular devices allowing some increase in the stability of DNA, in
normal conditions for these bugs. This problem is not completely known
yet. There are biochemical devices allowing a better protein stability
as well. But I remember of no enzyme that is able to catalyze
efficiently a biological reaction at temperatures above 120°C, otherwise
I may be mistakened. Still very very far from 200-300°C.
Among hyperthermophiles most studied are Pyrococcus furiosus and
Thermotoga maritima (see data bases). See R. Jaenicke (1996) FEMS
Microbiol.Letters 18, 215-224; E.L. Shock (1996) Ciba Found. Sympos.
202, 40-52.
Cheers
--
J. Pelmont, Grenoble
jean.pelmont at wanadoo.fr